1. Field of the Invention
The present, invention relates to an image processing apparatus required to control to match colors of images output from different devices, an image processing method, and a storage medium.
2. Description of the Related Art
In recent, years, the performance of printers that form images using an electrophotography system has improved, and models that, realize image quality that is equivalent to a printing press have appeared. However, such printers suffer from problems of a larger variation in the amount of formed colors than a printing press due to instability that is unique to the electrophotography system. In order to suppress this variation in amounts, a conventional electrophotographic printer executes calibrations by incorporating one-dimensional tone correction LUTs (Look Up Tables) corresponding to cyan (C), magenta (M), yellow (Y), and black (K) toners. Note that the LOT is a table that indicates output data corresponding to input data whose tones are divided at predetermined intervals, and can express nonlinear characteristics which cannot be expressed, by calculation formulas. The one-dimensional tone correction LUTs express output signal values on the printer side, which can express C, M, Y, and K input signal values, and the printer forms an image on a print sheet using toners corresponding to the output signal values.
The tone correction LUT generation processing will be described below. Charts based, on a plurality of data of different tones, which correspond to the C, M, Y, and K toners, are prepared, and are output by the printer. The charts output by the printer are read by a scanner, colorimeter, or the like, and the read values are compared, with target data, which are prepared, in advance, thus generating one-dimensional LUTs for correction.
Using the one-dimensional LUTs generated in this way, data respectively expressed by C, M, Y, and K unicolors can be corrected with high precision. However, even when tone characteristics of these unicolors are matched, it is difficult to guarantee colors of mixed colors such as red (R), green (G), and blue (B). Thus, a technique that focuses attention on a destination profile of ICC profiles specified by the International Color Consortium, and modifies it to correct, colors of mixed colors has been proposed (for example, see Japanese Patent Laid-Open No. 2006-165864). With this technique, a chart, generated using mixed colors is output by a printer, and is measured by a scanner or colorimeter. Then, based, on differences between colorimetric results and target values, an LUT (destination profile), which, is included in the ICC profiles and is required to convert a device-independent color space (L*a*b*) into a device-dependent color space (CMYK), is updated. Thus, colors of the mixed colors can be corrected. Note that L*a*b* is one of device-independent color spaces defined by the CIS (International Commission on Illumination), L* represents luminance, and a*b* represent hue and saturation. In addition, by generating a four-dimensional LUT used to correct CMYK, colors of the mixed colors can also be corrected.
However, the conventional technique for correcting the mixed colors is that for correcting colors of the mixed colors of a correction performing device itself, when mixed color characteristics of devices having different color reproduction ranges are to be matched, mismatching may often occur. When a corrected color of a certain device becomes a color which cannot be reproduced by that device as a result of processing for matching colors to those of another device, correction precision of that color is worsened. When a plurality of colors around a color close to a boundary of a color reproduction range are to be corrected using a correction result of that color, the correction result of the color also influences surrounding colors. Therefore, colors of the mixed colors between a plurality of devices having different color reproduction ranges cannot be matched.